FIG. 1 schematically depicts a touch panel sensing system, which includes an array of capacitance units 10 where external object movement will induce capacitance variation on parts of the capacitance units 10, and a sensing chip 12 where object movement induced capacitance variation will be sensed and processed such that object movement information can be generated for further use. The sensing chip 12 includes an array of sensing units 14 for sensing external capacitance variation, a multiplexer/analog-to-digital converter (Mux/ADC) 16 for converting sensed output into digital information, a digital signal processing unit 18 for filtering, calculating required sensed information, and a timing control unit 20, a microcontroller unit (MCU) 22 and an I/O peripheral unit 24 for control of whole system operation and information input/output.
Such a two-dimensional touch panel sensing system has been widely applied to various electronic products as an input device, while suffering problems such as multi-touch positioning and interference caused by moisture or water droplets. Sensing the mutual capacitance between trace lines is effective in facilitating multi-touch positioning and telling water droplets from operators' fingers.
U.S. Pat. Application No. 20090273573 and U.S. Pat. Nos. 6,452,514 and 7,352,192 have disclosed various mutual capacitance sensing structures and methods. However, these arts need a large signal generator, for example a pulse width modulation (PWM) pulse generator, for better output performance, or more complicated circuits for more accurate measurement.